This blog provides updated forecasts and comments on current weather or other topics

Wednesday, June 30, 2010

Fourth of July Forecast and the Upcoming Heat Wave

We are about to repeat an age-old Northwest weather pattern. People complain about the "unusually" cool and cloudy June. The weather prediction for July 4th calls for clouds and a chance of showers, and somehow the fireworks just squeak bye on a cool, but acceptable night. And then the miracle occurs. Like a switch being flipped, our weather warms dramatically. The lawns turn brown and watering our vegetables and plants is mandatory. The best weather in the nation takes hold for roughly 2-3 months.

And it is about to happen again.For the past weeks a persistent trough of low pressure has bedeviled the Northwest, bringing cooler and cloudier than normal conditions. But lets get one thing straight--June is typically NOT a good month west of the Cascades. Normal is lots of low clouds and hit and miss sunshine.

But as they say it is darkest before the dawn....and tomorrow will not be pleasant. A fairly strong upper level trough is now approaching (see figure) and it is associated

with considerable clouds and showers (see satellite picture). Tomorrow (Thursday) will not be nice. Lower 60sF.

A second weak trough comes through early Friday, leaving that day with scattered showers and a few sun breaks. Perhaps mid-60s

Saturday really should be decent, with little or no precipitation, partly cloudy skies and considerable sun and temperatures in the mid to upper 60s.

On Sunday, July 4th, the air will still be on the cool side and there will be lots of onshore flow; there could be some light, scattered precipitation, strengthened by a weak disturbance moving to our north early in the day. No guarantees. But no major storm.

But then the impossible will occur. Ridging in the eastern Pacific will build.

The pesky west coast trough will be no more and temperatures will warm rapidly on Monday and Tuesday.

Sun will return and temperatures will reach the seventies from Tuesday onward. Here is the upper level flow for Tuesday afternoon...a magnificent ridge.

Even lower to mid- 80s away from the water by mid-week. We are talking a significant heat wave and it will seem more so with all the cool weather we have been through.

Time to purchase a fan....

Finally, if any of you are interested, I will be one of the instructors this summer (August 5-8) at the North Cascade Institute's Northwest Naturalists Weekend: Weather, Wildfire and Biodiversity. I will provide a series of talks on NW weather and the other instructors will be talking about effects of wildfires and about lowland forests. Plus, hikes and canoe trips and good organic food in a beautiful location. For more information go to:http://www.ncascades.org/programs/seminars/course.html?workshop_id=1018

9 comments:

Cliff - You'd be doing a real service to >10,000 riders in the Seattle-to-Portland bicycle classing July 17-18 if you could give us some analysis of the likely weather for that weekend in a future post.

Cyclists will be concerned with temperature, precipitation, and especially wind speed and direction.

The ride starts 4:45am Saturday. The route is generally along the I-5 corridor, crossing the Columbia at Longview.

I think you might need superhuman powers not to complain about Junuary. After waiting 8 months for summer, and then knowing everyone in the country but you is basking in the sun and eating fresh tomatoes...

But of course, as soon as the temperatures hit about 78F, we will all complain about heat because we have been acclimated to 40-60F for so long. ;)

I tell newcomers all the time, Summer in W. Washington starts on July 5th, or the first Monday following the Independence Day weekend. They scoff, until it happens as scheduled. LAST year was the anomaly.I seem to recall seeing a chart a while back that showed 7/4 statistically being the wettest day of July/August.

Personally, I think there's a bit of July 4 "mythology" about Seattle-area (or just west of the Cascades in the Pac NW in general) that has developed that is misleading. Over the past 10 years, only in 2006 was there recorded measurable rain (.02). Five of those years (so exactly half) we had 75+ degree weather on July 4, (which does NOT include 2006, when we hit 75, though we had the bit of rain). The average temp at SeaTac is 74 for July 4, which itself says probably no rain. I think it's only when we compare ourselves with so many other part of the country that we feel like we too often get short shrift for our July 4 festivities.